I think it's somewhat silly to say that we want unlimited intelligence. We cannot, by definition, understand how being that intelligent would feel. Without challenges, life would be terribly boring. It would be impossible to keep our current personnality because our personnality is in part defined or influenced by our knowledge and our intelligence.
How you feel depends at more on your emotion systems than on your intelligence. We need challenges now because we are only capable of being interested in things that challenge us. However, this doesn't necessarily have to be so. We could, theoretically augment our intelligence while maintaining the feeling engagement with whatever interests us now.
As for whether our personality would be the same: that depends on how you choose to define your identity. Personally, I don't want to define myself by my limitations. As long as I had the same interests and values, and I wasn't
less intelligent then I am now, I'd consider myself the same person.